Hydrostatic extrusion of powder

ABSTRACT

RODS OR WIRE ARE PRODUCED FROM POWDER BY FORMING A BILLET COMPACTED TO GREAT DENSITY AND PROVIDED ON ITS SURFACE WITH A TEMPORARY, LIQUID-TIGHT BARRIER OF NONMETALLIC YIELDING MATERIAL. THE BILLET IS ENCLOSED IN A PRESSURE CHAMBER LOCATED ABOVE A DIE, WITHIN WHICH CHAMBER A LIQUID CAN BE COMPRESSED. THE COLD BILLET IS FORMED BY HYDROSTATIC EXTRUSION TO A CROSS SECTION DETERMINED BY THE NOZZLE OF THE DIE AFTER WHICH THE TEMPORARY BARRIER IS REMOVED. THE DEFORMATION IS CARRIED OUT UNDER SUCH PRESSURE AS TO PRODUCE A SUFFICIENT INCREASE IN TEMPERATURE TO SINTER THE POWDER.

Feb. Z, 1971 .1. NlLssoN HYDROSTATIC EXTRUSION OF POWDER Filed June 24,1968 du W V l Il //r, yA

INVENTOR. JAN Nl LS SON BY 3,559,271 HYDRSTA'HC EXTRUSON 0F POWDER JanNilsson, Robertsfors, Sweden, assigner to Allmanna Svenska ElektriskaAktiebolaget, Vasteras, Sweden Filed June 24, 1968, Ser. No. 739,487Claims priority, application Sweden, .lune 26, 1967, 9,071 67 Int. Cl.B22f 3/24 U.S. CL :E9-420.5 13 Claims ABSTRACT F DISCLOSURE BACKGROUNDOF THE INVENTION (l) Field of the invention The present inventionrelates to a method of producing rods or wire by means of hydrostaticextrusion, using powder as starting material.

(2) The prior art Many hard and brittle alloys which are difficult tomachine or not malleable (can be mechanically deformed only withdifficulty) consist of metals which, in unalloyed state, areindividually soft and ductile. If components of such alloys aremanufactured from powder mixtures by means of compression, andafterwards sintered so that an alloy is obtained or the constituents arebound together to give the finished component the desired properties,the components only need to be trimmed after they have become difcult tomachine. When manufacturing components from powder it is extremelydiicult to make them so compact that shrinkage during the sintering isso slight and uniform that the desired tolerance can be maintained orthat the material is sufficiently dense so that its properties can befully exploited. Particularly in the manufacture of long rod-shapedcomponents, it has been diieult to obtain high and uniform density sothat during sintering or compacting the alternations in dimension alongthe length of the rod are uniform and so negligible that the desiredtolerance can be maintained.

Rods have also been produced by extruding powder with the addition of abinder through the die. With previously known methods the addition of abinder has been necessary for the compression to take place underreasonable pressure and so that the powder is held together duringfurther treatment. The density of the powder is deteriorated due to thisaddition. The binder is removed before sintering or disappears partly orcompletely during the sintering and thus gives rise to spaces betweenthe powder particles or to shrinkage of the body resulting in poormechanical properties and diiiculty in maintaining small tolerance.

Hot extrusion of powder is also known. The high ternperature, oftenabove 1,000 C., causes considerable strain on the tools, however. Aswith most other hot plastic machining methods, it is difficult tomaintain small tolerance and satisfactory surface finish.

Patented Feb. 2, 1971 SUMMARY oF THE INVENTION ICC According to theinvention tubes, rods or wire are manufactured by means of hydrostaticextrusion of a billet consisting of powder of a single material or amixture of powders of different materials to provide the desiredcornposition. No binder is added. Usually metal powder is used, butcertain oxide powder mixtures of metal and oxide powder or metal powderwith oxide coating may also be used.

Normal commercial powder of copper, aluminium, iron, or the like havinga particle size under 150g (under mesh) can be used. According to themethod the powder is shaped into a billet and compacted to great densityand provided on its surface with a temporary, liquid-tight barrier ofnon-metallic, tenacious material, after which the billet is shaped intoa bar or tube by means of hydrostatic extrusion in equipment comprisinga pressure chamber, a die inserted in this chamber with a nozzle to givethe billet the desired cross-section, a pressure medium enclosed in thepressure chamber and a pressure-generator to generate the pressurenecessary in the pressure chamber for the extrusion. After the extiusionthe temporary barrier is removed which, during the extrusion process,prevents the pressure medium from penetrating into the pores of thebillet.

The temporary barrier suitably consists of a plastic material having ahardness of at least 60 Shore A. With this or greater hardness theplastic has such resistance that it is not pressed into the poresbetween the powder particles of the billet. Plasticized PVC (polyvinylchloride) is an extremely suitable material. The plastic layer formingthe barrier can be applied by bringing the heated billet into contactwith a powder or grains of the plastic and afterwards possibly insertingit in a furnace and treating it there so that the plastic layer obtainsthe desired density and hardness. It is also possible to apply theplastic by dipping the billet in a melt or solution of the plastic or byspraying molten plastic or plastic dissolved in a solvent onto thebillet. Before extrusion the billet should be compacted, for example bymeans of hydrostatic compacting, to a density which is at least 60% ofthe theoretically possible density, that is the density of a solidbillet of the same material.

For the compressed rods to obtain a crack-free surface it is necessaryto use pressure above a certain minimum value. To a certain extent thispressure depends on the material. Usually the more brittle the materialis the higher will be the required extrusion pressure. The requiredextrusion pressure can be obtained in most cases by making the extrusionratio suiciently great. This :is normally designated R and is the ratiobetween the crosssection Ao of the billet and the cross-section A of theextruded product. Thus RzAo/A. with a small extrusion ratio a crack-freeproduct can be obtained under compression with a counter-pressure on theoutput side of the die. Compression with a counter-pressure may benecessary when extruding brittle materials or when, for some otherreason, it is desirable or necessary to operate with low extrusionratio. The counter-pressure demands correspondingly higher pressure inthe pressure chamber and greatly complicates the equipment. Highercounter-pressure than 4,0005,000 bar is hardly possible. Withcounter-pressures of this magnitude R 3 is desirable if a crack-freeproduct is to be obtained. With R 6 it is usually possible to obtain acrackfree product without using counter-pressure during the extrusion.With very high extrusion ratio a temperature increase due to deformationis obtained of such magnitude that the powder is sintered while it isbeing pressed out through the die. When aluminium powder is beingextruded an extrusion ratio R 60 is required for sintering. If theextrusion takes place under counter-pressure the nozzle on the outputside is connected to a pressure chamber in which a constantcounter-pressure can be maintained with the help of control means forthe purpose.

The method enables products to be manufactured from powder which havegreater density than is possible with previously known methods. Thedensity involves more intimate contact between the powder particles,which enables the body to be more easily sintered. Similarly, the goodparticle contact involves less alteration in dimension during sinteringand produces a nal product with better mechanical properties.

The powder used may consist of several substances, each of which isplastically formable. Upon extrusion a rod is formed in which theconstituents, during the subsequent sintering, form those alloys whichgive the material the desired properties. In many cases it is possibleto utilize the constituent alloying substances better and thus producethe desired properties in the finished product while using less of thealloying substances which usually constitute the most expensive particlecomponents in the powder mixture.

Another advantage which is gained by the method according to theinvention is that rods can be produced having desired dimensions andsmall tolerance from material which in the form of a nished alloy cannotbe plastically machined and therefore cannot be given the desireddimension yby rolling or forging. On the other hand a powder mixturehaving the same composition can be shaped by extrusion to rods, assumingthat at least a certain proportion of the constituents are individuallyductile. Examples of the above-mentioned alloys are:

Iron-aluminium with high Al content Iron-nickel-cobalt with high Ni andCo content.

Dispersion-tempered products with extremely good properties can also bemanufactured with advantage according to the method. Particles of hardmaterial, for example certain oxides, are then mixed into the powder orare included in specially treated powder where the surface of the powderparticles is coated with an oxide. During the extrusion process theseparate particles are greatly deformed and the hard substances brokendown to very small particles which are also very evenly distributed inthe iinished rod. This means that the content of dispersion-temperedsubstances can be kept low since it is the free path between particlesof the additional material which determines the properties of theproduct. With a low content of additional material its negative effectwill be negligible. It is thus possible according to the method tomanufacture aluminium conductors having great mechanical strength butapproximately the same Conducting capacity as conductors of purealuminium. If a billet is extruded having a content of 0.5% A1203 it ispossible to obtain a final product with an ultimate tensile strengthab=26, proof stress ay2=24 and elongation measured on a length of 5X thediameter S5=l0%. It is also possible to manufacture aluminium productshaving a high content of A1203 which can be used in temperatures up to400 C.

Products of this type have previously been extremely diicult tomanufacture and consequently very expensive. A Swiss product is soldunder the name SAP-aluminium. Material for gas turbine pistons havinggreat mechanical strength at high temperatures, based on nickel withThO2 as the dispersion-tempered material seems also possible tomanufacture according to this method.

The shape of the extrusion nozzle is important for the quality of thesurface of the extruded rod. The nozzle should have a conical entrancepart the acute angle of which should be greater than 25 and less than 90depending on the material of the billet to be extruded. For mostmaterials an acute angle of around 45 is suitable. The Calibrating partof the nozzle below ythe entrance cone should have a certain minimumlength if the best result is to be obtained. A length of approximately lmm. has been found suitable and sufficient for materials extruded sofar.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in thefollowing with reference to the accompanying drawing which showsschematically a pressure means for carrying out tne method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS- In the drawing 1 designates ahigh pressure chamber, extrusion chamber, formed by a steel cylinder 2which is strongly pre-stressed with the help of a surrounding tape or awire sheath 3, an extrusion nozzle 4 and a piston 5. The piston 5 isconnected to a piston l6 in a cylinder 7 with a lid `8 through which thepiston 5 passes. The lid 8 is attached to the cylinder 7 by bolts 9. 10is a yoke which supports the cylinder 7 and absorbs pressure from itduring the extrusion. The cylinder rests on a table 11 which is joinedto the yoke by means of columns, not shown in the drawing. The nozzle 4is arranged in a holder 12 sunk into the table 11. Below the extrusionnozzle 4 is a counter-pressure chamber 13 consisting of a tube'14 whichis connected to the holder 12 and attached to the table 11 by means offlanges 15 and 'bolts 16. At its lower end the tube is closed by a lid17 which is easily removed, for example by a bayonet catch, so that theextruded rods can be removed from the counter-pressure chamber 13. Thepressure chamber 13 is connected for pressure control by means of thechannel 18 to a cylinder 19 with a piston 20 which is in turn connectedto a piston 21 in a cylinder 22. The lid 23 is attached to the cylinder22 by means of bolts 24. In the lid 23 are channels 25 and a valve seat26 against which a valve body 27 is pressed by the spring -28, thetension of which can be regulated by the screw 29 so that the desiredcounter-pressure can be obtained in the chamber 13. Through the channel30 and conduits, not shown, the cylinder 22 is connected to a pressuresource so that between pressure operations the plstons 20 and 21 can bemoved to approximately the position shown in the drawing. 31 is a billetto be extruded and 32 a rod which has left the pressure nozzle 4 andreached the counter-pressure chamber 13. The cylinder 7 is connected bythe channels 33 and 34 to a pressure source for operating the piston 6,The space is, by means of the channel 41 and the -pipe fittings, notshown in the drawing, in connection with a collecting container forhydraulic Huid, 35, 36, 37, 38 and 39 are seals between constructionelements in the hydraulic system.

When carrying out the method with the help of the equipment shown in thedrawing, the operation is as follows:

A billet 31 consisting of a powder of one or usually several materials,normally metals, is shaped and surrounded by a yielding, liquid-tightcasing. It is then compacted in a pressure chamber by means of ahydrostatic pressure. After compacting, the casing is removed and oneend of the billet is shaped to fit the nozzle or die 4. The billet isprovided with a new, thin, liquid-tight casing, for example a layer ofvarnish. The billet is then inserted in the pressure chamber 1 and thepunch 5 is pushed by the piston 6 into the cylinder 2 so that pressureis generated in the chamber 1 which, when it reaches a certain value, isable to deform the billet so that it is pressed or extruded through thenozzle 4 and a rod 32 is obtained. This has extremely high density andgreat accuracy of dimension. In this way very small and uniformshrinkage is obtained during the subsequent sintering and the need forfinal processing is minimal.

In the example shown the extrusion takes place under counter-pressure.The rod 32 which leaves the nozzle 4 is pressed or extruded into achamber 13 in which a constant counter-pressure is maintained during theextrusion process. This pressure is maintained by a pressure-regulatingmeans connected to the chamber 13 having a differential piston with thepistons 20 and 21 and a control valve with a valve body 27 actuated bythe spring 2S, which permits liquid to pass out of the cylinder 22 whenthe pressure has reached a certain predetermined value. When theextrusion process is complete the lid 17 is removed and the extrudedbillet taken out. The piston is returned to its upper position bysupplying liquid to the space below the cylinder 6 in the cylinder 7through the channel 33. The pistons 20` and 21 are returned to theposition shown in the drawing by supplying liquid to the cylinder 22through the channel 30. A new working cycle can then be commenced.

The invention is not limited to the above-described method. Severalvariations and modifications are possible within the scope of thefollowing claims.

I claim:

1. Method of producing rods or wire of desired configuration from powderby hydrostatic extrusion, comprising the steps of:

(a) forming a billet from powder;

(b) compacting the billet to great density;

(c) applying a temporary, liquid-tight barrier of nonmetallic, yieldingmaterial directly upon the surface of the powder billet, said barrierpreventing pressure medium from penetrating into the pores of the billetduring hydrostatic extrusion;

(d) inserting the billet in a pressure chamber of an extrusion press,said pressure chamber having a die with an opening to shape a productand containing a pressure medium surrounding the billet;

(e) generating a pressure in said pressure medium sufficient to drivethe billet through the die; and thereafter (f) removing the temporarybarrier from the extruded billet.

2. Method according to claim 1, in which the temporary barrier consistsessentially of a plastic layer with a hardness of at least 60r Shore A.

3. Method according to claim 2, in which the ternporary barrier consistsessentially of plasticized PVC (polyvinyl chloride).

4. Method according to claim 1, in which the temporary barrier consistsessentially of a plastic layer which is applied by bringing a heatedbillet into contact with powder or grains of plastic.

5. Method according to claim 1, in which the temporary barrier consistsessentially of a plastic layer which is applied by dipping in a melt orin a plastic dissolved in a solvent.

6. Method according to claim 1, in which the ternporary barrier consistsessentially of a layer of plastic material which is applied by sprayingon a plastic or elastomeric material dissolved in a solvent.

7. Method according to claim 1, in which before the extrusion the billetis compacted to a density which is at least of the density of a solidbillet of the same material.

8. Method according to claim 1, in which the ratio R between thecross-section of the billet and the crosssection of the extruded productis greater than 3:1.

9. Method according to claim 1, in which the hydrostatic extrusion takesplace underV such high pressure that the deformation provides suicienttemperature increase to sinter the powder.

10. Method according to claim 9, in which when extruding a billet ofaluminium powder, the ratio is 60: 1.

11. Method according to claim 1, in which a powder consistingessentially of a mixture of substances which are individuallyplastically deformable, is formed by hydrostatic extrusion into a rod inwhich the constituents form alloys during subsequent sintering whichgive the rod material the desired properties.

12. Method according to claim 1, in which a powder ofdispersion-tempering products is mixed into the metal powder.

13. Method according to claim l, in which a billet extruded through thenozzle is subjected to a counter-pressure in a chamber connected to thenozzle externally.

References Cited UNITED STATES PATENTS 3,076,916 2/ 1963 Koppius29-420.5UX 3,344,507 10/1967 Green 29-420.5 3,390,985 7/1968 Croeni etal. 29420.5X 3,407,475 10/ 1968 Koppius L29- 420.5

JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner U.S.Cl. X.R. 72-710

